Anyone know when the Mopar cars switched from leaf springs to trailing arm rear suspension? I took some pictures of an older Grand National (maybe a Winston Cup) car this week and it still had leaf springs in it. The car is probably from the late 60's or early 70's.

K frame car with torsion bars, Mopar power steering, etc. Obviously a factory frame car but heavily modified. The drive side torsion bar had a jack on it that could be adjusted by the driver to change the preload. Production lower control arms, drum brakes, tubular upper control arms, spline type anti-sway bar, etc. Pretty cool stuff to look at but the rear leaf springs surprised me. I just thought everyone had gone with the pickup truck type suspension back in the 60's.